The present invention relates to a DC machine such as a DC homopolar motor using the magnetic field generated by a superconductive coil, or more in particular to a superconducting DC machine having a high electrical efficiency with the armature voltage increased for a reduced current value.
Conventional DC homopolar motors, not utilizing superconductivity, use an iron core for intensifying magnetic fluxes and a multiplicity of current-collecting brushes arranged longitudinally of the armature. This has increased both the weight and volume of the DC machine as a whole. The flux density of the magnetic field generated from the field coil by the use of an iron core gap has its own limitation. The resulting requirement for using a low voltage and a large DC current causes a large electrical loss and a low efficiency.
In an effort to overcome this shortcoming, the introduction of a motor using superconductivity has been considered. The operation of a motor under superconductive state, however, essentially requires a low voltage and a large current, thus making it necessary to take a large current load into consideration. In other words, protective means such as a cooling system is required to cope with the large Joule heating by a large current.